The Spatial Structure of Party Competition: Party Dispersion within a Finite Policy Space

Using the Comparative Manifesto Project (CMP) data for twenty established parliamentary democracies, the authors have studied the relationship between number of parties in a party system and party dispersion. They found that as the number of parties in the system increases, the dispersion of parties also increases, but only up to a point. The boundaries of a finite issue space appear to expand up to at most five parties. In addition, once the number of parties in the party system was controlled for, they found that electoral rules have no direct effect on party dispersion. Thus, their findings validate the theoretical predictions of spatial theory while at the same time highlighting surprising ways in which the policy space is constrained.